Sr2CrO3FeAs的非化学计量和磁结构
Non-stoichiometry and the magnetic structure of Sr2CrO3FeAs
摘要：
合成了具有四方晶系Sr 2GaO 3CuS型结构的铁砷化物Sr 2CrO 3FeAs，并用中子粉末衍射重新确定了其晶体结构。与以前的X射线晶体学研究相反，在FeAs 4/4层中发现了铬和铁的混合占据（93+/-1%Fe：7+/-1%Cr）。我们认为，部分Cr掺杂在Fe位的原因是没有自旋密度波异常和超导性在这种化合物。通过中子极化分析的附加实验揭示了在~100 K以下的短程自旋关联和在T_N = 36 K以下的长程反铁磁有序，磁传播矢量q =（1/2，1/2，0）。Cr ~（3+）离子在磁空间群C_Pmma'（a' = a-b，b '= a+b，c'= c）中形成C型共线磁结构，其中Cr ~（3+）离子占据4g（0，1/4，z）Wyckoff位置。磁矩沿正交a '轴排列。在3.5 K时，Cr ~（3+）亚晶格的有序磁矩为2.75+/-0.05 mu_B。
英文摘要：
The iron arsenide Sr2CrO3FeAs with the tetragonal Sr2GaO3CuS-type structure was synthesized and its crystal structure re-determined by neutron powder diffraction. In contrast to previous X-ray crystallographic studies, a mixed occupancy of chromium and iron was found within the FeAs4/4 layer (93+/-1% Fe : 7+/-1% Cr). We suggest that the partial Cr-doping at the Fe site is the reason for the absence of a spin-density wave anomaly and superconductivity in this compound. Additional experiments via neutron polarization analysis revealed short-range spin correlations below ~100 K and long-range antiferromagnetic ordering below T_N = 36 K with a magnetic propagation vector of q = (1/2, 1/2, 0). The Cr3+ ions form a collinear magnetic structure of the C-type in the magnetic space group C_Pmma' (a' = a-b, b'=a+b, c'=c), where Cr3+-ions occupy the 4g (0, 1/4, z) Wyckoff position. The magnetic moments are aligned along the orthorhombic a'-axis. At 3.5 K, an ordered magnetic moment of 2.75+/-0.05 mu_B for the Cr3+-sublattice was refined.
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